I have a 10' by 16' Woods KD. My flock went through temperatures as low as -30C for several days, multiple times through the winter. I did NOT cover the front NOR did I use any heat other than what the birds themselves generate and a heating cord (21 watts) that I have under the nest box to avoid freezing eggs (except for the ones they lay on the drop board).
Wow, that's harsh--the weather, not you. But these are newly-hatched chicks, with no adults. Aren't they going to be a lot more sensitive to deep cold than the adults? All the information I've seen about new hatchlings says that they are very cold sensitive at first, and not well insulated until they feather out. And I did lose two CX one night when it was very windy and freezing. The others all looked stressed that morning, too.
The first three days, I put (red) heat lamps on 24 hours per day. The next three, I only put them on if the temp got near freezing. At one week, I took away the cardboard corral and let them have the run of the 8x12 coop. And as I said, I stapled cardboard over the big window when temps were at freezing and the winds were over 60mph.
When I have adults, I won't cover the windows no matter what the weather says. If a hen has chicks, I'm assuming she'll keep them from freezing. Just now, the darned CX look like they are half-plucked already, they are growing so fast. I'm taking away their food at night, and they are ready to eat
me when I come into the coop in the morning!
But all heat is off now--and probably forever. Next winter, I'm going to follow your plan, and see how it goes.